This inventions ling adjacent printed circuit boards, more particularly, this invention relates to using optical signals to connect adjacent circuit boards.
In a typical computer cabinet there are multiple printed circuit boards (PCBs), each attached to a back plane. In the context described herein, PCB is used as a generic term to describe any board or module which may require one or more signals be connected to another board or module. The back plane provides not only power for the PCB, but also may provide buses or pathways for signal connection between and among PCBs as well as provide physical support.
The use of back planes may suffer as a technique for moving fast signals from one PCB to another because of inherent inadequacies. Signals generated from any location on the PCB must be routed to the back plane connector, the signals must be transmitted through the back plane connector to the back plane and then through a similar reverse path to the ultimate location on the receiving PCB. This signal path is subject to parasitic capacitance, noise, transmission line effects and other such effects which degrade the signal, and significantly slow it down. Current electrical techniques for compensating for these inadequacies are predicted to become inadequate within a decade.
One way to alleviate this problem is to augment PCB to PCB connections using a flex ribbon which allows a connection from one PCB to another and by-passes the back plane. One end of the flex ribbon is attached to one PCB and then the other end of the ribbon is attached to the other PCB.
In computer systems today, minimizing space is important for many reasons. In such systems, PCBs are located as close together as possible. In some instances the spacing between PCBs is around three or so inches. Additionally, these PCBs are designed to be inserted and removed without affecting system performance.
Using a flex ribbon in such a computer configuration is problematic for at least two reasons. First, the space between PCBs is too small for a technicians to attach a flex ribbon, insert the PCB and than attach the flex ribbon to the second PCB. One solution to this problem is to place the flex ribbon connector on the edge of the PCB. Second, a flex ribbon typically uses wires to transmit signals. In computer systems where speed is important, the inherent slowness of current wiring schemes may not meet system speed performance criteria. Also, when placing a flex ribbon connector on the edge of the PCB, additional time is added to the signal path because the designer must move the signals to the end of the PCB and signal speed is slower on a flex ribbon compared to a PCB.
What is needed is a way to connect adjacent PCBs together that is faster than current techniques and works in the tight confines of rack mounted computer systems.
In accordance with the invention there is provided an optical interconnect to connect at least one signal on one electrical component to a second electrical component using optical guides. In one aspect, the optical interconnect optically connects two electrical components by having a first frame which is flexibly connected to one electrical component. The frame includes a plurality of optical guides which are connected to the electrical component either electronically or optically. A second frame, coupled to the second electrical component also contains a plurality of optical guides. A mechanical guide assembly positions the first frame and the second frame so that at least one optical guide in the first frame is optically coupled to a respective optical guide in the second frame. The optical guide in the second frame connects to the second electrical component providing a path for a signal from the first electrical component to the second electrical component.
The optical guides could be tubes and the tubes could be adapted to hold receive lenses to focus the light. Furthermore, the lens could be a GRIN (graded index) lens. The lens is approximately 1.0 mm, but could also be in the range from about 0.25 mm to about 1.2 mm. If a lens is in the first frame, it could have a length less than the length of the tube and preferably positioned in the portion of the tube further from the other frame.
In one aspect of the invention, an optical fiber connects a vertical cavity surface emitting laser (VCSEL) on the first electrical component to the GRIN lens. A lens could be disposed on the VCSEL. In another aspect of the invention, a wire connects a signal from the first electrical component to a VCSEL disposed at the first frame. A lens could be disposed on the VCSEL between the VCSEL and the second frame.
In yet another aspect of the invention, the second frame contains GRIN lenses that focus the light to a photodetector coupled to the second electrical component. A lens could be disposed on the photodetector between the photodetector and the GRIN lens.
In still another aspect of the invention, an optical fiber connects a photodetector on the first electrical component to the GRIN lens. A lens could be disposed on the photodetector. In another aspect of the invention, a wire connects a signal from the first electrical component to a photodetector at the first frame. A lens could be disposed on the photodetector between the photodetector and the second frame.
In yet another aspect of the invention, the second frame contains GRIN lenses that focus the light from a VCSEL coupled to the second electrical component. A lens could be disposed on the VCSEL between the VCSEL and the GRIN lens.